There were advertisements for beer and bikinis, jokes about flatulence, and a halftime peep show featuring Janet Jackson.

But a 30-second ad about the Bush administration's run-up of the federal deficit? Now that's too much. That was the one thing CBS would not allow.

With the ad producers - a liberal advocacy group MoveOn.org - calling CBS's decision not to air its commercial during the Super Bowl "censorship," and CBS countering that, actually, it has "for decades" shunned ads that touch upon "controversial issues of public importance" - attention turned to the murky market of advocacy advertising.

And even as the Federal Election Commission (FEC) sat this week to decide whether to put new limits on soft money collection by nonparty political advocacy groups (which would expand the scope of the 2000 McCain-Feingold campaign finance law), the question of whether or not the networks would, or could, limit the airtime they give to these groups remained unanswered - controversial.

"Child Play," the ad in question, was the winning entry in a contest run by MoveOn.org. Set to slow music, it features a montage of children working in menial adult jobs - a pretty blond girl with a ponytail toils on a factory line, a small boy hauls trash in the early morning - and asks: "Guess who's going to pay off President Bush's $1 trillion deficit?"

MoveOn.org, which had promised that the winning entry would be shown during the Super Bowl broadcast, came forward with the $1.8 million to pay for 30 seconds of airtime - only to betold 'no thank you' by CBS's standards and practices department.

"The standards and practices department reviews all ads," explains Dana McClintlock, senior vice president of CBS communications. "And in this case decided not to accept the MoveOn ad because it was an advocacy ad."

According to what standards? "According to their sensibilities," says Ms. McClintlock.

CBS guidelines are "designed to prevent those with means to produce and purchase network advertising from having undue influence on 'controversial issues of public importance,' " explains CBS in a statement. "From the network's perspective, we believe our viewers are better served by the balance and perspective such issues can be afforded within our news programming."

CBS is no different from any other network on this question. While there is no Federal Communications Commission (FCC) lawregarding advocacy ads, each network has its own guidelines.

Susan Sewell, a spokeswoman for ABC says: "We don't take them." Asked to define an advocacy ad, she responds: "Gun control, abortion, and things like that." ABC policies, she says, have been around "as long as I've worked here."

In 1997, ABC rejected ads for a cruise line targeting gays during the coming-out episode of Ellen. In 2000, both ABC and CBS rejected an ad that encouraged viewers to "fight for your right to a safe and legal abortion," and People for the Ethical Treatment of Animals (PETA) has tried for years - unsuccessfully - to get its ads aired during the Super Bowl.

Liberal groups, incidentally, are not the only ones complaining. Last fall, CNN rejected two spots from pro-Israel groups, and in 2000, CBS turned down spots by the Christian website iBelieve.com.

Further confusing the current issue is the fact that CBS - after rejecting the MoveOn.org ad - ran a White House anti-drug spot during the very same Super Bowl. Then, a few weeks later CBS pulled a public service ad on Medicare, arguing that it was too pro-Bush - only to later return it to the screen again after the content was tweaked.

And just to complicate matters further, local network affiliates (where advocacy groups are most apt to place ads) have their own policies and guidelines.

"Local stations we own," says a CBS statement, "are free to accept or reject such advocacy advertising for their own airtime based on how they believe such decisions serve public interest."

Such lack of uniformity makes for confusion - accusations of partisanship.

"The bottom line problem is that the networks will never tell you explicitly how they define advocacy ads," says Timothy Karr, director of "Media for Democracy" a nonpartisan citizen initiative to monitor media coverage of the presidential elections. "They will never publish a set of rules so it's impossible for the public to determine whether they are being fair or not - and the criticisms will continue."

Wes Boyd, MoveOn.org's co-founder calls CBS's practices "arbitrary and capricious," and points out that Viacom - CBS's parent company - is lobbying to lift FCC limits on media consolidation - an effort the Bush White House supports. "Any way you slice it, it looks like CBS is playing politics with the right to free speech," says the group's website.

But there are other freedoms at stake as well, point out some observers. "We have to be mindful of the First Amendment and find a balance between pushing for more political discourse in the media - which we are for - and allowing networks to retain editorial judgment," says Amy Wolvertine, media program director of the nonpartisan Campaign Legal Center.

She and most observers agree, however, that such discussions seem likely to become even more heated in the election year ahead.